1. Field of the Invention
The present invention relates to an apparatus for measuring ammonia concentration, a system for measuring ammonia concentration, a system for treating an exhaust gas, and a method for measuring ammonia concentration.
2. Description of the Related Art
Hitherto, ammonia sensors to detect ammonia concentrations in target gases such as exhaust gases of automobiles have been known. For example, Patent Literature 1 describes a multi-gas sensor including an ammonia sensing section having a pair of electrodes arranged on a solid electrolyte body. Formula (2) based on a mixed-potential formula is known as the characteristics of the electromotive force (EMF) of a mixed potential cell including solid electrolyte body and a pair of electrodes (for example, Non-Patent Literature 1).
                    [                  Math          .                                          ⁢          1                ]                                                            EMF        ∝                              RT                          2              ⁢              F                                ⁢                      (                                                            2                  3                                ⁢                ln                ⁢                                                                  ⁢                                  p                                      NH                    ⁢                                                                                  ⁢                    3                                                              -                                                1                  2                                ⁢                ln                ⁢                                                                  ⁢                                  p                                      O                    ⁢                                                                                  ⁢                    2                                                              -                              ln                ⁢                                                                  ⁢                                  p                                      H                    ⁢                                                                                  ⁢                    2                    ⁢                    O                                                                        )                                              (        2        )            (where                EMF: the electromotive force of the mixed potential cell        R: a gas constant [J/(K·mol)]        T: the temperature of the mixed potential cell [K]        F: the Faraday constant [C/mol]        pNH3: ammonia concentration in a target gas        pO2: oxygen concentration in the target gas        pH2O: H2O concentration in the target gas)        